1. Field
This patent document relates to a semiconductor device and a method for operating the same.
2. Description of the Related Art
FIG. 1 is a block diagram illustrating a plurality of data pads DQ<0:N> and a plurality of data buffers 110_0 to 110_N which are included in a semiconductor device. The plurality of data buffers 110_0 to 110_N may buffer data inputted to the corresponding data pads and output the buffered data as outputs OUT<0:N>.
Each of the data buffers 110_0 to 110_N receives data from the corresponding data pad through a first input terminal IN1, receives a reference voltage VREF through a second input terminal IN2, buffers the data of the corresponding data pad using the reference voltage VREF, and outputs the buffered data. Each of the data buffers 110_0 to 110_N outputs a high signal when the voltage of the corresponding data pad (hereafter, referred to as input voltage) is higher than the reference voltage, and outputs a low signal when the input voltage is lower than the reference voltage VREF. That is, the output of each of the data buffers 110_0 to 110_N has a logical value which varies with reference to the reference voltage VREF. Each of the data buffers 110_0 to 110_N includes a differential amplifier may amplify the difference between two input signals.
In general, semiconductor circuits including differential amplifiers in data buffers have offsets which occur due to errors in design, the semiconductor fabrication process, packaging errors, or the external environment. Because of offsets in differential amplifiers, the output of the data buffer varies with reference to an incorrect voltage, as opposed to the correct reference voltage VREF. For example, the output of the data buffer may vary with reference to an erroneous voltage level that is higher than the reference voltage VREF, or vary with reference to an erroneous voltage that is lower than the reference voltage VREF. The variation in the output of the data buffer depends on the magnitude of the offset, and the offsets of the differential amplifiers may be different from one another.
FIG. 2 is a diagram illustrating the problem of the semiconductor device of FIG. 1.
FIG. 2 illustrates the input ranges R_0 to R_N of data corresponding to the maximum margin that the plurality of data buffers 110_0 to 110_N can have. The data inputted to the respective data pads DQ<0:N> have the same swing SW.
In order to obtain the maximum margin, the reference level of each of the data buffers 110_0 to 110_N must be positioned in the center of the input range R_0 to R_N of the data inputted to the data buffer. The reference level indicates the reference level of an input voltage, at which an output of the data buffer transits. For example, when the reference level of a specific data buffer is X[V] and the swing of data inputted to the specific data buffer is Y[V], the input range of the corresponding data must be set to X±Y/2 [V].
As illustrated in FIG. 2, the plurality of data buffers 110_0 to 110_N have various reference levels RL_0 to RL_N different from the ideal reference voltage level VREF due to offsets. Thus, the input range of data in which the maximum margin can be obtained may differ for each of the data buffers 110_0 to 110_N. The semiconductor device uses the reference voltage VREF to buffer data. In order to prevent failures of the data inputted through the data buffers 110_0 to 110_N, the data inputted to the semiconductor device must be included commonly in the input ranges of all the data buffers 110_0 to 100_N with reference to the reference voltage VREF. Thus, the data inputted through the data buffers 110_0 to 110_N may have a common range CR. The common range CR has a smaller value than the swing SW of the data. This is, due to an offset difference between the respective data buffers 110_0 to 110_N, the data input margin of the semiconductor device may be reduced.